Conventional electrode structure for resistance welding utilized in a resistance welding machine can be found, for example, in Japanese Patent Application Publication No. H10-43870 as a movable-electrode structure in a resistance welding apparatus for nut. This electrode structure includes a movable electrode (upper electrode) and a fixed electrode (lower electrode) that are made of non-magnetic material and arranged vertically so as to face each other, and a guide pin of the movable electrode is inserted into a through-hole of a nut disposed between the electrodes to hold the nut.
After this holding, the movable electrode is lowered along with the nut to position the nut in a predetermined welding position of the workpiece on the fixed electrode. In this case, the electrode structure is configured as follows for preventing the nut from falling off the guide pin during the nut being lowered. That is, an air passage is formed inside the guide pin, and a plurality of air outlet holes communicating with the air passage are formed on a circumferential surface at an end (lower end) of the guide pin. Pressurized air is supplied to the air passage to blow air upward from the air outlet holes at the lower end to a lower surface of the nut, to prevent the nut from falling off.